CRUK- Beatson Institute, Glasgow, United Kingdom.
Fundación IMDEA-Nanociencia, Campus de Cantoblanco, Madrid, Spain.
Elife. 2021 Jan 13;10:e64624. doi: 10.7554/eLife.64624.
The ADP-ribosylation factor-like 3 (ARL3) is a ciliopathy G-protein which regulates the ciliary trafficking of several lipid-modified proteins. ARL3 is activated by its guanine exchange factor (GEF) ARL13B via an unresolved mechanism. BART is described as an ARL3 effector which has also been implicated in ciliopathies, although the role of its ARL3 interaction is unknown. Here, we show that, at physiological GTP:GDP levels, human ARL3GDP is weakly activated by ARL13B. However, BART interacts with nucleotide-free ARL3 and, in concert with ARL13B, efficiently activates ARL3. In addition, BART binds ARL3GTP and inhibits GTP dissociation, thereby stabilising the active G-protein; the binding of ARL3 effectors then releases BART. Finally, using live cell imaging, we show that BART accesses the primary cilium and colocalises with ARL13B. We propose a model wherein BART functions as a bona fide co-GEF for ARL3 and maintains the active ARL3GTP, until it is recycled by ARL3 effectors.
ADP-核糖基化因子样蛋白 3（ARL3）是一种纤毛病 G 蛋白，可调节几种脂修饰蛋白的纤毛运输。ARL3 通过其鸟嘌呤交换因子（GEF）ARL13B 激活，但其激活机制尚未解决。BART 被描述为 ARL3 的效应物，也与纤毛病有关，尽管其与 ARL3 的相互作用尚不清楚。在这里，我们表明，在生理 GTP:GDP 水平下，人 ARL3GDP 被 ARL13B 弱激活。然而，BART 与无核苷酸的 ARL3 相互作用，并与 ARL13B 一起有效地激活 ARL3。此外，BART 结合 ARL3GTP 并抑制 GTP 解离，从而稳定活性 G 蛋白；然后，ARL3 效应物的结合释放 BART。最后，通过活细胞成像，我们表明 BART 可进入初级纤毛并与 ARL13B 共定位。我们提出了一个模型，其中 BART 作为 ARL3 的真正共 GEF 发挥作用，并维持活性的 ARL3GTP，直到被 ARL3 效应物回收。
